At present, sewage treatment plants in urban areas produce a large a amount of excess sludge and in the meantime, food processing industry produce a large amount of industrial wastewater every year. In addition to carbohydrates and fats, protein is the major organic components of the excess sludge and wastewater from food processing industry. Proteins account for over 40% of the solid components of excess sludge (SS) and protein-containing wastewater is produced in large quantities in the process of food processing (e.g. soy, whey and fish). It is one of major issues in the field of environmental protection to make the excess sludge and sewage with high protein content be harmless and became useful resources. Meanwhile, hydrogen can be widely used as a kind of clean energy. There will be a broader prospect if the biological production of hydrogen via anaerobic fermentation of wastes with high protein content could be accompanied by making the wastes be harmless and become useful resources simultaneously.
Under anaerobic conditions, proteins can be firstly hydrolyzed into peptides and amino acids, and then converted into short-chain fatty acids with production of hydrogen gas in acidification stage. The products by acidification are finally converted into methane in methanation stage. To obtain hydrogen gas as an intermediate product, it is necessary to inhibit the activity of methanogenic bacteria and to restrict the fermentation process to the acidification stage and further to inhibit the activity of other hydrogen-consuming bacteria except methanogenic bacteria. However, unlike carbohydrates, protein has a slow rate of degradation and an incomplete degree of degradation under anaerobic conditions. The hydrolysis process is a rate limiting, step in the process of anaerobic degradation of proteins.
UV light, especially UV light-C, provides a kind of physical methods for protein denaturation. The natural structure of proteins can be damaged after absorption of UV light by tyrosine, tryptophan and phenylalanine in the proteins and protein unfolding may occur, which will facilitate protein hydrolysis and subsequent biological production of hydrogen.